1. Field of the Invention
The present invention relates to a filter device for filtering a contaminated fluid that contains particles.
2. Description of the Related Art
In a machine tool for precision machining, for example, a fluid such as a coolant is used to lubricate or cool machined portions. Since particles of dust, carbon, etc., as well as chips, become mixed into the fluid as a workpiece is machined, a fluid of this type is gradually contaminated to a point at which it becomes unusable.
There has been proposed a filter device in which magnetic impurities in the contaminated fluid are captured by magnetizing, by means of a solenoid coil, chips as filter elements that are produced by the machine tool, for example, in order to filter the contaminated fluid. A conventional filter device is described in Jpn. Pat. Appln. KOKAI Publication No.  11-77479.
Since the conventional filter device described above uses the filter elements that are formed of chips, it is subject to a substantial dispersion in filtering accuracy. Besides, filterable particles are limited to metallic particles, such as chips of a magnetic material, so that the device cannot fulfill its filtering capacity for non-magnetic particles of carbon, aluminum, etc., especially ultra-fine particles of several tens of μm or thereabout.
If the filter elements that are formed of chips are used, moreover, it is hard to clean the filter elements to recover the filtering capacity when the filtering capacity is reduced, since the surfaces of the chips are very rough. Even though the filter elements (chips) themselves are not costly, therefore, these filter elements (chips) must be frequently changed, thus entailing labor and high cost.